Jaylen Brown has been there before, but the playoffs are a new experience for rookie Jayson Tatum. School is definitely out, but Jayson has never played like a first-year guy. He came into the League looking like a seasoned pro, and he has improved since then.

Not so for his Jay-Team partner, Jaylen Brown. Jaylen struggled a bit in his rookie season, but he has really stepped up his game in his sophomore season. He will be ready and prepared for the round-one meeting with the Milwaukee Bucks, and much is expected (and needed) from him.

For Tatum to be relied on so heavily by a contending team is noteworthy. His contributions in the regular season have been critical to his team's second-place finish in the Eastern Conference. His shooting early in the season was commendable, but it became predictable by defenders. That has changed. He had developed that hesitation, herky-jerky style that made Paul Pierce such a tough cover, and that has made a difference. Predictability is seen as a weakness in the playoffs and will be exploited. Why do you think Aron Baynes and Greg Monroe have been practicing their three-point shooting lately? This is MassLive's Tom Westerholm on the Jay-Team's challenges:

The playoffs -- the biggest test of the season for both Brown and Tatum -- are here. There's no more surprising opponents with a newly effective 3-point shot, or catching defenders unaware with blow-by moves off the dribble. There's just execution against defenses that are prepared exclusively for you.

Brown experienced it once before.

"I was just telling (Tatum) about my experiences from last year," Brown said. "Like, the more exaggerated version was Washington. It would be like the game would be tied and then one or two mistakes would happen or one bad shot and they'd go on a 16-0 run, and that was the difference in the game. In the regular season you don't really see it like that."

So it definitely is Jay-Team Time. The game starts at 1:00 P.M. EST, and TD Garden will be loud. These two youngsters are the future of the Celtics, and they certainly will be put to the test today.